Study On The Combination Of Wall Thermal Storage And Ventilation Cooling Technology For Office Building

Nowadays there are a lot of researches about building energy storage and night ventilation domestic and overseas. But as there are so many factors that influence the night ventilation, most of which are uncertain, the existing researches about night ventilation are in the primary theory stage, and most of them focus on the analyses of the mechanisms of the ventilation, the combination with heat storage and climate cooling potential. There are rarely any works about taking reasonable air supply and air distribution ways to remove the heat stored in building envelope effectively. The indoor thermal comfort is guaranteed mainly by changing the ventilation rate; result in high ventilation rate and big amount of ventilation quantity. However, in the life cycle of a building, the cost of designing is much lower than that of the make up work after it. Therefore it is significant to engineering practice to form a complete and effective strategy for night ventilation building design and night ventilation operation.The office building in southwest China was selected as the study object of night ventilation. As the outdoor cooling air in the night is used to remove the stored heat in building envelope and indoor thermal mass, the vent mainly works in the night, which is suitable to office building considering the occupancy property of office building. But when it comes to the residential building, things are different since the noise of vent and the tolerance of air supply rate are vital for resident under night ventilation. Above all, the office building is used in daytime and vacant in the night, which makes it the best candidate for the usage of night ventilation.To begin with, the mechanism and calculation method of wall's transient heat transfer was introduced, the factors which influence the thermal performance of building envelope are analyzed, including thermal resistance, heat transfer coefficient, heat storage coefficient, heat inertia index, attenuation multiple and delay time. The result was that the wall heat storage property cannot be judged by single factor, but by comprehensive consideration of the combined influence of all the factors. Then put forward to a wall's thermal performance evaluation system using heat storage and indoor air temperature as the criteria.Then the numerical simulation tool EnergyPlus was used to analyze a group of walls in different heat insulation forms with same thickness. The result showed that the performance of external thermal insulation wall is better than that of internal thermal insulation wall and non-thermal insulation wall. The analysis of a group of walls in different thickness draw a conclusion that the attenuation multiple and delay time increases along with the wall's thickness. The delay time of external insulation wall is shorter than the four walls. For the external insulation wall, it has no advantage in night ventilation. Similarly, the heat storage increases along with the thickness of walls. In the heat release stage, the heat storage of non-insulation wall drops sharply. However, the trend of external insulation wall is much gentle. When the outdoor air temperature decreases, the non-insulation wall releases the stored heat to the outdoor environment quickly, while the external insulation wall could not pass the heat to the outdoor as the thermal insulation of the external insulation layer.More over,reconstruct the experimental room in the roof of third floor of urban construction and environmental engineering faculty in Chongqing University. The wall and indoor air temperature is measured in natural condition and night ventilation condition and compared with the numerical simulation. The result shows that there is a certain error between the test and the simulation, but it's in the acceptable range.In addition, Fluent was used as the numerical simulation software to analyze night ventilation. Choose slot outlet as the air supply method, and then study the factors which influence the night ventilation effectively in Guiyang and Chongqing. The result shows that although external insulation wall has a steadier room temperature after ventilation, it has less temperature time delay than the thickened walls. As the thickness of wall increases, the time span which the room air temperature remains comfortable is longer. When the wall thickness increases to 300 mm it will be comfortable in the office work time without air conditioning. But for residential building, the external insulation wall is recommended in consideration of the whole day's comfort conditions. At the same time, the analysis found that the PPE and COP cannot be the evaluate criterion of energy saving potential of night ventilation. It also found that the most energy saving wall is not always the most economic and best indoor comfort wall. As the air supply rate increases, the indoor air temperature decreases faster, the time span of comfort condition is. The earlier the air supply time is, the higher the heat exchange rate between supplied and exhausted air is. But the higher is the amount of vent electric consumption. The comparison of simulation results in Guiyang and Chongqing found that the night ventilation potential of Guiyang is much higher than that of Chongqing.Finally, took orthogonal experiment with three factors that influence the night ventilation effect in Guiyang. Considering the economical and comfort efficiency, the recommended night ventilation parameter of wall thickness is 300 mm, air supply time is 23:00-9:00, and air supply rate is 3m /s.